The invention relates to optical spectroscopy and single- and multi-element analysis by the emission or absorption of optical radiation.
Compared to other spectrometers, Echelle spectrometers have the advantage of higher resolution with the same focal length or of a smaller and more compact structure with the same resolution. In Echelle spectrometers, a dispersion prism is generally used to separate the orders, so that a two-dimensional spectrum arises in the focal plane (DE-1909841). A wavelength is here associated with every position in the focal plane, and vice versa. The parameters of the components, such as the grid constant, the prism angle, and the wavelength-dependent index of refraction and the mutual distances and angles of the components, as well as the air pressure (altitude of the erection site above sea level) and the temperature, all enter as parameters in the functional relationship between position and wavelength. By purposefully changing the parameters, an Echelle monochromator can be tuned as regards wavelength. In that case, generally only one exit slit exists in the focal plane. According to DE-1909841, the dispersion prism is turned about its roof edge for this purpose, and the Echelle grid is turned about an axis that is approximately parallel to the groove as well as about an axis that stands thereon and that is perpendicular to the optic axis.
With a polychromator, light of different wavelengths (spectral lines) emerges through different exit slits which are arranged in the focal plane, where the components remain nearly stationary. The mutual position of the exit slits is suitably fixed by a mask. The emerging light is conducted by fiber-optic light guides onto the receivers (DD-WP 217626). The theoretical values for the positions of the spectral lines, which then can be implemented in the exit slit mask, are derived from the theoretical values for all the parameters which simultaneously secure the highest imaging quality (DD-WP 226962). For this reason, when Echelle spectrometers are mass produced, the position of the spectral lines must be reproduced very precisely. Because the positions of the spectral lines depend on very many parameters, very close tolerances must therefore be required for each parameter. This demands great expenditure in the fabrication of the components and in the adjustment of their mutual position.
For reasons of mechanical stability, the large number of setup parameters does not permit making provision for adjusting all these setup parameters. The components must be adjusted once furing setup, and then must be fastened so that they can no longer change their position as a result of transport or the like. If the indispensable checking of the line positions reveals too large a deviation of the spectral lines from the exit slits, the totality of setup and component parameters must be examined and must be corrected if necessary. Component parameters can be corrected in this arrangement only by replacing the component.
For the above-mentioned reasons, mass production of Echelle spectrometers with an exit slit mask is associated with very great expense. Furthermore, when the spectrometer is repaired (when replacing components), the necessary adjustment of the component must be repeated with expensive adjustment means, until the positions of the spectral lines agree with the exit slits. Furthermore, the use of the spectrometer is limited to a narrow temperature and pressure range.